A highly active and chemoselective homobimetallic ruthenium catalyst for one-pot reductive amination in water

Abstract

Two new Ru(II) compounds, bimetallic [(p-cymene)2(RuCl)2L1] (Ru1) and monometallic [(p-cymene)(RuCl)L2] (Ru2) (where L1=2,2'-((1E,1'E)-((3,3',5,5'-tetraisopropyl-[1,1'-biphenyl]-4,4'diyl)bis(azaneylylidene))bis(methaneylylidene)) diphenoxide) and L2=(2,6-diiso-propylphenyl)imino)methyl)phenoxide) incorporating Schiff base ligands have been synthesised and characterised by various spectroscopic and analytical...

Dinuclear Ru(II) Schiff Base Complex Catalyzed One-Pot Synthesis of Quinolines through Acceptorless Dehydrogenative Coupling of Secondary Alcohols with 2-Nitrobenzyl Alcohol

“…This interaction plays a pivotal role in shaping the reactivity of the catalyst and stabilizing active intermediates formed during the catalytic cycle, as demonstrated in our recent investigation on the reductive amination reaction. 55 Similarly, in this study, the absence of an induction period for Ru1 can be ascribed to its enhanced activity, facilitating the formation of ruthenium hydride species that is required for the reduction of nitro compounds to amines. This rapid activation of the precatalyst in Ru1 is attributable to the cooperative interaction between the two metals, which is otherwise absent in the mononuclear catalyst Ru3.…”

“…Thus, it is apparent that the dinuclear complexes present a distinctive advantage over their mononuclear counterparts owing to their ability to facilitate electronic interactions between the two metal centers. This interaction plays a pivotal role in shaping the reactivity of the catalyst and stabilizing active intermediates formed during the catalytic cycle, as demonstrated in our recent investigation on the reductive amination reaction …”

“…Condensation of either 2,2′,6,6′-tetraisopropylbenzidine or commercially available diisopropylaniline with pyridine-2-carboxyldehyde produces ligands N , N ′-(3,3′,5,5′-tetraisopropyl-[1,1′-biphenyl]-4,4′-diyl)­bis­(1-(pyridin-2-yl) methanimine) ( L 1 ) and N -(2,6-diisopropylphenyl)-1-(pyridin-2-yl)­methanimine ( L 2 ), respectively. , By combining these ligands with a ruthenium p-cymene precursor complex, new catalytic systems have been prepared in good yields by adopting synthetic protocols used earlier for other ruthenium Schiff base complexes. − In a typical synthesis, [Ru­( p -cymene)­(μ-Cl)­Cl] 2 reacts with L 1 in the presence of sodium tetrafluoroborate or ammonium hexafluorophosphate in ethanol at room temperature to produce Ru1 or Ru2 (Scheme ). Similarly, the use of L 2 produces Ru3 .…”

“…In the cases of Ru1 and Ru2, a single absorption broad band around 380 nm was associated with the dπ → π* charge-transfer transition and was attributed to a metal-to-ligand chargetransfer (MLCT) transition (Figure 2). 55,56 Molecular Structure of Ru1 and Ru3. Single crystals of Ru1 and Ru3 complexes suitable for X-ray diffraction analysis were grown by recrystallization of the crude product from an ethanol:acetone mixture (4:1) under ambient conditions by slow evaporation of the solvent.…”

“…However, our recent investigations on the reductive amination reaction utilizing a bimetallic Ru(II) catalyst has shed light on this matter. 55 Through a combination of experimental data and computational studies, we developed a catalyst model in which one Ru center exhibited reactivity while the other remained inactive. This model demonstrated that the simultaneous engagement of both Ru centers facilitated the formation of active catalyst species, thereby accelerating product formation through structural and electronic cooperativity.…”